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A dissolution-precipitation mechanism is at the origin of concrete creep in moist environments

Summary

Macroscopic creep of cementitious calcium–silicate–hydrate (C–S–H) gels influences long-term deformation of concrete structures, especially under sustained load in moist environments. This Journal of Chemical Physics article advances a nanoscale explanation: basic creep at relative humidity ≥ 50% with fixed moisture content follows a stress-driven dissolution–reprecipitation mechanism at grain contacts, analogous to pressure solution in geological minerals. The argument is built from micro-indentation creep rates, vertical scanning interferometry tracking surface height under load, and atomistic simulations of C–S–H compositions spanning the compositional variability relevant to real pastes. The synthesis aims to connect composition-dependent dissolution propensity from simulations to measured macroscopic creep rates.

Methods

Experiments. Basic creep is probed at relative humidity \(\geq 50\%\) with fixed moisture content using micro-indentation creep rates and vertical scanning interferometry of surface height under load—the combination is used to connect macroscopic creep response to nanoscale processes at grain contacts.

Atomistic simulations. The authors build Pellenq-type C–S–H supercells spanning Ca/Si ratios, hydrate interlayers with Grand Canonical Monte Carlo (GCMC) against bulk water at constant volume and room temperature, then propagate ReaxFF molecular dynamics with a 0.25 fs timestep so that interlayer water can dissociate into hydroxyls. Structures are relaxed toward zero stress before further analysis. Topological constraints’ enumeration then analyzes MD trajectories at 300 K to classify rigid versus floppy network modes; those MD segments are described as canonical (constant-volume) sampling in the sense of fixed-cell thermalization at 300 K, with detailed thermostat couplings and production run lengths (multi-ns segments in the cited protocol papers) spelled out in Refs. 29 and 35 rather than re-tabulated here. Periodic in-plane models follow the defective tobermorite construction summarized in Section II.E of the PDF. Experimental dissolution benchmarks in the article reference 1 bar-class aqueous conditions for VSI rate measurements, distinct from the zero stress mechanical relaxation applied to the atomistic cells before further MD assessment. N/A — umbrella / metadynamics / replica exchange; N/A — applied electric field. N/A — standalone new ReaxFF training in this paper—the authors “retain the original ReaxFF potential” from prior parametrizations while focusing on dissolution–creep correlation.

Interpretation. The combined protocol links atomistic kinetics to macroscopic creep metrics for basic creep at relative humidity \(\geq 50\%\) with fixed moisture content, arguing for a stress-driven dissolution–reprecipitation picture at nanoscale grain contacts rather than viscoelastic grain sliding alone in that regime.

Findings

Creep rates correlate with computed dissolution rates across the C–S–H chemistries examined, supporting dissolution–precipitation as a governing mechanism under the stated humidity and loading conditions rather than only viscoelastic flow of grains. The framework links composition-dependent nanoscale kinetics to long-timescale macroscopic deformation, with implications for durability modeling when moisture and stress are simultaneously present. Other creep mechanisms may still contribute outside the emphasized regime; the paper focuses where moisture-enabled dissolution is expected to be active. Interpretations hinge on the relative humidity \(\geq 50\%\) window and fixed moisture content assumptions stated for the experiments, because concrete creep mechanisms can switch sharply when environmental constraints change.

Limitations

Idealized atomistic models omit full microstructure complexity (porosity distribution, ionic strength variations, alkali effects) present in real concrete.

Reader notes (MAS / retrieval)

Pair with cement microstructure pages when translating nanoscale dissolution arguments to paste-scale creep forecasts.

Also link theme-oxides-silica-ceramics for broader silicate context.

See also the JCP figure supplements for creep curves.

Relevance to group

Provides experiment-integrated atomistic perspective on silicate materials and aqueous interfaces adjacent to oxide and cement literature in the corpus.

Citations and evidence anchors